Production of diolefins



Filed June 20. 1942 Patented June 1l, 1 946 Jean P.

Delaware Jones, Bartlesville, Okla., -assignor to Phillips Petroleum Company,

a corporation of Application June 20, 1942, Serial No. 447,803

3 Claims.

This invention relates to the production of dlolefln hydrocarbons from hydrocarbons heavier than methane. More particularly it relates to the production of diolefin butadiene and pentadiene, from aliphatic hydrocarbons having two and three carbon atoms per molecule. It also relates to the production of such dioleflns from benzene and the like.

hydrocarbons, such as An appreciable number of dioleflns such as butadiene and pentadiene have been known to the art for a number of years. These have been produced in a number of ways which have includedcracking of heavier oils, the interreaction of acetylene and ethylene to form butadiene, catalytic or thermal conversion oi.' alcohols, both of the same number of carbon atoms per molecule as the desired vdiolen and of a fewer number of carbon atoms per molecule, as well as the dehydrogenation of the corresponding olefins which in turn may have been produced by the dehydrogenation of the corresponding-paraiiins. Dioleflns have also been reported as being present in the pyrolysis products of light hydrocarbonsincuding even methane. There are enormous quantities of such lighter hydrocarbons which are potentially available for the production of diolefin hydrocarbons'but apparently most of the commercial installations and processes to date have been one of the more involved types previously mentioned rather than the direct conversion of cheap and abundant light hydrocarbons to dioleflns.

I have found that I can successfully produce substantial yields of low-boiling dioleflns of the type mentioned from lighter gaseous hydrocarbons by a suitable combination of high-temperature conversion steps, to be more fully disclosed hereinafter, with certain steps for the conversion of aromatic hydrocarbons, such as benzene, to diolefin hydrocarbons.

In one modification of my invention an ethanepropane fraction is converted at an elevated temperature to produce an optimum yield of unsaturated hydrocarbons of low molecular weight, the eiliuent is passed to a separating means wherein an unsaturate-containing Cz-Ca fraction is separated from a heavier hydrocarbon fraction which may contain some diolefin hydrocarbons and from a lighter fraction which contains hydrogen, the unsaturate-containing Cz---Cal fraction is passed to a second conversion step at an elevated ternperature and low pressure to form an optimum yield of diolefin hydrocarbons, benzene which is inherently produced in said second conversion is with hydrogen produced in the first conversion step to cyclohexane and cyclohexane sc produced cracked to low-boiling diolefin hydrocarbons, and diolefins, particularly butadiene, are recovered from the eilluent of the last step.

In another modification of my invention benzene from an outside source is hydrogenated to cyclohexane and cyclohexane cracked to butadiene and a lighter hydrocarbon fraction. Such lighter hydrocarbon fraction kcomprises substantial quantities of C2 and C3 hydrocarbons which are separated therefrom and subsequently passed to a conversion step for production of additional butadiene.

separated from the eluent thereof, hydrogenated 66 IIt is an object of my invention to convert aliphatic low-boiling non-diolefinic hydrocarbons into low-boiling diolefin hydrocarbons.

Another object of my invention is to convert cyclic hydrocarbons into low-boiling diolefin hydrocarbons.

Another object of my invention is to convert aliphatic hydrocarbons of two and three carbon atoms per molecule to diolefin hydrocarbons.

A further object of my invention is to convert ethane and propa-ne to butadiene.

Further objects and advantages of this invention will become apparent from the accompanying disclosure and discussion.

I The features of my invention will now be disclosed and discussed in connection with the accompanying drawing, which illustrates diagrammatically by way of a flow sheet the manner of practicing my invention, together with auxiliary steps which may be incorporated with various modifications of it, and which serves to exemplify` my invention.

In one modification of my invention a light gaseous hydrocarbon material, such as a mixture comprising ethaneand propane, is passed from any suitable source through conduit I0, controlled by valve Il. to a dehydrogenator I2, which will generally be a cracking and dehydrogenating furnace. This mixture is heated and cracked in coil I3 at a low pressure of the order of 5 to 50 pounds per square inch absolute and at a temperature of 1300 to 1600 F. for a time suicient to form an optimum amount of ethylene and propylene with only minor amounts of light oils. When desirable, a suitable dehydrogenating catalyst, not shown, may be used in place of or along with the non-catalytic cracking operation, especially when a heavier stock is being dehydrogenated to produce higher boiling unsaturates, but for the charge stocks here specifically de- .scribed the simple non-catalytic cracking and The light fraction containing` A iight oil fraction containing hydrocarbons of more than three carbon atoms per molecule may be removed from my process through conduit 20, controlled by valve 2|. Usually. hydrocarbon material passed through conduit contains recoverable amounts of dioliiin hydrocarbons, in which case I prefer to pass such material through .conduit`22, controlled by valve 23, to separating means 24 in which diolefin hydrocarbons, such as butadiene and pentadiene, are separated and can be recovered through conduits 62 an'd 64, respectively. v

A light hydrocarbon fraction containing essentially Cz-'Cs unsaturated hydrocarbons is removed fromseparator I6 through conduit 32, controlled by valve 33. Such low-boiling unsaturated hydrocarbons are passed to the heating and/or conversion zone 35 represented by a tube coil in a suitable heating unit 34. The material charge to the conversion zone 35 may beaugmented by similar low-boiling unsaturated hydrocarbons introduced from any suitable outside source through conduit 38, controlled by valve 39, which may at times constitute the sole charge to the process. In one modification the zone 35 is primarily a heating zone operated in conjunction with a conversion chamber 42 to which it is joined Iby con- When` duits 36 and 40 controlled by valve 4|. using such a conversion chamber, the material passing through conduit 32 is rapidly heated in zone 35 to a temperature only suiiicient to initiate an uncatalyzed reaction, which takes place in conversion chamber 42. This chamber is preferably insulated to preclude substantial heat transfer through the walls thereof, and the inlet conduit 40 and the outlet conduit 43 are preferably so placed that a direct passage of the contents from the inlet to the outlet is not favored but rather so that a dilution and mixing of the chamber contents with the incoming mixture is favored. Reaction eiliuents from chamber 42 are passed vthrough conduit 43 controlled by valve 44 to a suitable separation means 24 by means of conduit 36. When the conversion chamber 42 is not used and the desired extent of conversion is effected in zone 35, eilluents therefrom may be passed directly through conduit 36 and valve 31 `to the lseparating means 24 -by closing valve 4| in conduit 40.. When conversion chamber 42 is used valve 3'! in conduit 36 remains closed.

The conversion eiected in' zone 35'and/or 42 is such as to produce from low-boiling unsaturated hydrocarbons charged through conduit 32 an optimum yield of low-boiling diolen hydrocarbons of the nature of butadiene, pentadiene, and cyclopentadiene. Optimum conditions for such a` reaction exist when the conversion is conducted in a temperature range suitable for` the production of low-boiling aromatic hydrocarbons for a period of time such that only a minor Portion Qi such aromatics are produced. Morespecincally I prefer to operate within a range of about 1300 to 1700 F.. preferably between about 1375 and 1550 F. for a period of time such that the eiiluent contains not more than about 10% by weight of C4 and heavier hydrocarbons which are a result of synthesis reactions. However, of course, an appreciable amount oi' C4 and heavier hydrocarbons will Ibe producedby such synthesis reactions, and it has been found that the diolenn content does not approach a desirable value until at least about 3% by weight of the eiiluent consists of such synthetic C4 and heavier hydrocarbons. The overall synthesis reactions are exothermic with highly unsaturated charge stocks and endothermic when the charge contains relatively large amounts of saturated hydrocarbons, and suitable means for removing or adding heat may be provided to maintain a fairly uniform reaction temperature.

In the conversion zone 36 and/or 42 the pressure should be low throughout the reaction, generally not in excess of about 50 pounds per square inch absolute and may be subatmospheric although pressures lower than about 1.5 pounds per square inch absolute are generally not practical. With some relatively more unsaturated charge stocks, the formation of butadiene, andthe like, will result to a substantial extent from polymerization-type reactions, and pressures as high as pounds per square inch may be employed. However, such pressures also tend to promote formation of .other and less desired products of higher molecular weight. With such pressures, the throughput per unit of time is also increased. With relatively less unsaturated charge stocks. lower pressures are more desirable. Low partial pressures with the total pressure somewhat above atmospheric, may be readily employed by using diluent gases, which may be gases such as nitrogen,methane or other suitable gases which are substantially unreactive under the conversion conditions, or which may be in part or entirely gases such as steam carbon dioxide,v which are not strictly reactants but whose 'presence appears to suppress or compensate for undesired side reactions such as the formation of tar and heavy carbonaceous material. When such diluents are used, the extent of conversion discussed above shouldk be calculated on a basis free of such diluent, or of compounds formed from it.

. Mention has been made of the fact that lowboiling unsaturated hydrocarbons from an outside source may be charged to conversion zones 35 and/or 42 by means of conduit 38 controlled by valve 39. `Material charged through conduit 38 may contain essentially Cz-Ca olen hydrocarbons although it usually also contains substantial amountsv of Cz-Ca paraiiln hydrocarbons. When an essentially unsaturated hydrocarbon material from an outside source is converted to diolens according to my process I prefer to pass such material through conduit 45 controlled by valve 46 to heating coil 50 in furnace 41. Conditions in heating coil 50 are similar to those discussed in connection with coil 35 when the latter is used to heat hydrocarbon material passed through conduit 32 and such heated material is subsequently converted in' conversion chamber 42. Low boiling unsaturated hydrocarbons so heated in coil k50 are passed through conduit 5| controlled by valve 52 and through conduit 40`to conversion chamber 42 wherein conditions are such as have been discussed in connection with material charged thereto through conduit 40 from heating lmay be passed to enorme coil 35 when little or no conversion occurs in 4coil35.

Reaction efiluents passing through conduit 38 to separating means 24 aretreated therein in such a manner that various types of hydrocarbons are segregated. In one preferred manner of practicing my invention, a substantial portion of the Ca and C3 hydrocarbons are separated in means 24 and returned to heating and/or conversion zone 35 by means of conduits 53, 38 and 32 when valve 54 is open. Insome instances such material heating zone 50 through conduits `53, 55 and 45 when valve 56 is open and valve 54 is partly or entirely closed. This is particularly true when such material contains essentially unreacted unsaturated hydrocarbons. In other cases when the material in conduit 53 contains essentially ethane and propane in combination with only relatively small amounts of corresponding olefins, such material is preferably returned to cracking coil I3 through conduitv I0 by means not shown in the drawing.

Light gases, although present in small quantities in separating means 24 and containing hydrogen and methane, are removed from separating'means 24 through conduit 68 controlled by valve BI. When desirable such light gases are admixed with the light gases in conduit 38 which are ultimately charged to hydrogenator 82.

Diolefin hydrocarbons which comprise essentially C4 and C5 dioleflns as produced/according to my process are removed from separating means 24 through conduits 82 and 64, respectively, controlled by valves 63 and 85. respectively. Aromatic hydrocarbons inherently produced in heating and/o1` conversion coil 35 or conversion chamber 42, when operating according to the conditions ,disclosed herein for the production of dioleiins, are separated in means 24 into a benzene fraction and a heavier aromatics fraction. A fraction containing still heavier material and comprising essentially tar is removed from separating means 24 through conduit 12 controlled by valve 13. 'A hydrocarbon fraction containing essentially aromatic hydrocarbons having higher boiling points than benzene is removed from separating means 24 through conduit controlled by valve 1I and' an aromatic hydrocarbon fraction containing essentially benzene is removed from separating means 24 through conduit 14 controlled by valve 15.

The aromatic hydrocarbon fraction containing essentially benzene is passed via conduit 14 to hydrogenator 82 wherein benzene is converted to cyclohexane by treatment under non-destructive hydrogenation conditions with a hydrogenrich material produced in dehydrogenation and cracking coil I3 and passed to hydrogenator 82 from separator I6 by means of conduits 25 and 3U and valve 3l. When the hydrogen supplied from coil I3 is insufficient for carrying out the necessary hydrogenation or when dehydrogenation, such as would be carried 'out in coil I3, is omitted-from my process hydrogen from some convenient outside source may be supplied to hydrogenator 82 through conduit 80 controlled by valve 8|.

When the benzene fraction recovered from separating means 24 through conduit 14 contains impurities which would be deleterious to a hydr0genat0n Catalyst if allowed to come in contact therewith, such impurities are preferably removed from said benzenel fraction before being passed to hydrogenator 82 in equipment and means not shown in the drawing. Such impurities can be removed from the benzene fraction by suitable fractional distillation, treatment with an aluminum halide type of compound, caustic washing, and/or water washing such as.

would be obvious to any skilled operator in the art. f

At times it may be desirable to admix benzene from an outside source with the benzenefraction recovered from separating means 24. Such additional benzene is conveniently added to my process through valve 11 and conduit 18. When more benzene is produced by my process.- than -can be suitably hydrogenated, valve 11 may be operated in such a manner that it can also be used as an outlet valve for said excess benzene.

The conversion effected in hydrogenator 82 is A such as to produce an optimum yield of cyclohexane from benzene by utilizing hydrogen and benzene produced in previous conversion steps. Such a reaction is preferably conducted in the presence of a hydrogenation catalyst with a charge stock that is substantially free from material which would tend to poison the hydrogenation catalyst as has been discussed herein. In the presence of a nickel-alumina-copper catalyst similar to that described in U. S. Patent 2,242,627; optimum conditions for such a catalytic reaction exist when the conversion is conducted in a temperature range bet-Ween 200 and 600 F. and preferably between about 250 and 500 F. at flow rates between about 0.5 to 10 volumes of fresh charge stock per volume of catalyst per hour and preferably at flow rates of 1.0 to 5.0 volumes of fresh charge stock per volume of catalyst per hour when the conversion is effected in the preferred temperature range. Pressures in the hydrogenator 82 should be relatively high since the hydrogenation reaction is favored by high pressures. Pressures as high as 2000 to 3000 pounds per square inch gage have been -found advantageous in some cases. Also, pressures as low as 50 to 100 pounds per square inch gage have been observed to be sufficiently high to produce substantial amounts of hydrogenation. I prefer, however. to operate at pressures between 450 and 1000 pounds per square inch gage in the preferred temperature and flow rate ranges mentioned.

The amount of hydrogen admixed with the hyr drocarbon charge passed to hydrogenator 82 will be such that the hydrocarbon effluent consists primarily of cyclohexane, with little unreacted benzene. I prefer to conduct/the hydrogenation by recycling cyclohexane so that the combined hydrocarbon charge to the catalyst chamber 82 contains 10 to 50 per cent benzene,

- of benzene with the cyclohexane charged to the cally benzene from cyclohexane.

subsequent conversion step, and when' incomplete conversion of benzene to cyclohexane is effected, separating unit 81 will comprise any combination of means for the separation of an aromatichydrocarbon fraction from a naphthenchydrocarbon fraction, in this instance, 'specili- Such a separation is usually brought about by selective sol- Y by means of noncatalytic conditions.

vent extraction methods which are well known to the art. Separatingl unit 81 will include absorbers and strippers to'bring about the desired separation and will generally not' be a' single.

piece of equipment as represented in the4 drawing. Benzene separated in unit 81 is removed ltherefrom through conduit 88 controlled by valve 89 and returned to conduit 16 and hydrogenator 82 for further conversion to cyclohexane. When cyclohexane is recycled, as mentioned previously, this may be done through conduit 88. The light gases separated in unit 81 are Withdrawn via line 'I'he pro-V tween about and 60 per cent of the cyclohydrocarbon is converted per'pass. .As high as 85 -per cent, of the theoretical of diolens are produced from the hydroaromatics undergoing conversion.

When the catalytic conversion is employed, coil 93 is a heating coiland a major portion of the conversion occurs in catalyst chamber 100 containing material which acts as a catalyst for said conversion. Hydroaromatics heated to a catalytic reaction temperature pass through conduits 94 and 96. controlled by valve 81, to catalyst chamber |00. After being subjected therein to conditions as discussed for the catalytic step. eiiluent therefrom, containing the desired diolens, is passed through conduit |0| controlled by valve |02 to conduit y94 and thence to separating means |03. When only noncatalytic conversion duction of butadiene in coil 93therefolre, may

not only be from the conversion of cyclohexane but also from the conversion offpartially hydrogenated aromatics, such as cyclohexene, methylcyclohexene, and cyclohexadienes, vfor example.

The conversion of hydroaromatics to diolefins may be either catalytic or/noncatalytic and I have found that in the preparation of diolefins from cyclohexane, for example, the conversion is preferably carried out in the presence of a catalyst although it is entirely within the scope of my invention to convert hydroaromatics to diolefins When noncatalytic conversion is employed I prefer to operate coil 93 under conditions of low pressure such as between about 1.5 and 100 pounds per square inch absolute and preferablybelow atmospheric pressure and at a temperature between 1050 and 1550" F. and preferably between about 1200-and 1450 F. The time of reaction will vary with the extent of conversion desired. Under any v,given condition of temperature and pressure within the preferred range of operation, long contact time usually results in a greater extent of conversion than shorter contact times. In some instances I have found that the presence of extraneous material, such as steam, enhances the desired conversion to diolefins.

I prefer however to convert cyclohexane or any other hydrogenated aromatic hydrocarbonto a diolen in thepresence of a catalyst, such as a dilcultly reducible metal oxide, for example, oxides of -the alkali metals or alkalineearth metals or the vanadate, uranate, phosphate, aluminate, chromate, or tungstate salts of these metals. Also, oxides of scandium, zirconium, titanium, tungsten, yttrium, lanthanum, molybdenum, thorium or uranium are suitable for use according to the present invention for the conversion of hydrogenated aromatic hydrocarbons to diolefln hydrocarbons. The temperature employed for the'catalytic reaction should be at least 1000 F. and preferably not greater than 1500 F. The preferred temperature range is between 1100 and 1400VF. Pressures similar to those discussed in connection with the preparation of diolens from hydroaromatics in the noncatalytic conversion step are employed in said catalytic step. Contact times are such that beis employed, valve 91 is closed and eiiluent from coil A93 passes through conduit 94 and valve 95 directly to separating means |03.

Separating 'means |03 will comprise a number of individual separating units from which desired fractions are segregated. Light gas undesirable for further treatment in my process, such as methane, is recovered from means |03 through conduit |2 and valve ||3. When such gas contains larger amounts of hydrogen, said hydrogen may be passed to hydrogenator 82 by means not shown and employed therein as discussed.

A normally gaseous hydrocarbon fraction comprising essentially ethylene is removed from means |03 through` conduit H6 and may be passed either by lines ||4 and 32 to coil 35 or by line 45 to coil 50 by suitable control of valves ||5 and ||1 in conduits ||4 and H6, respectively, to be treated in either or both of said coils under conditions as hereinbefore discussed. Unconverted cyclohexane or other hydroaromatic may be returned to coil 93 through conduit |04 controlled by valve |05 as recycle stock. Butadiene is removed as a product .of the process from separating means |03 through conduit I0 controlled by valve Cs diolens and heavier aliphatic hydrocarbons may be removed from means |03 through conduit |06 controlled by valve |01 and subsequently treated las may appear desirable, such as by the separation of Cs diolefins from heavier aliphatics.

Iclaim:

1. The ,y process of converting a hydrocarbon charge consisting essentially of C2 to C: paraiiins to butadiene which comprises converting said charge to C2 to C3 olefins.by dehydrogenating same at an elevated temperature and a low pressure, separating from the effluent a light gaseous fraction containing essentially hydrogen and also a fraction containing essentially Cz to Ca olens, converting said last-named fraction to butadiene and benzene by subjecting it to an elevated temperature and a low pressure fora time such that by subjecting it to an elevated temperature and low pressure, recovering butadiene from the resulting en'luent and also a fraction containing essentially said ethylene formed in said last converting step, and feeding said ethylene fraction to said second converting step in admixture with said C2 to C: oleiin fraction recovered from the eiiiuent of said first-named converting step.

2. 'I'he process of converting a hydrocarbon charge consisting essentially of Cz to C3 paraiilns to butadiene which comprises converting said charge to Cz to Ca oleiins by dehydrogenating the same at a temperature of from 1300 to 1600 F. and at a pressure of from 5 to 50 pounds per square inch absolute, separating fromthe efiiuent a light gaseous fraction containing essentially hydrogen and also a light hydrocarbon fraction containing essentially C2 to Ca oleflns, converting said last-named fraction to butadiene and benzene by subjecting it to a temperature of from 1300 to 1700 F. and a low pressure for a time such that at least 3% and not more than 10% by weight of C4 and heavier hydrocarbons based on the weight of the resulting eiiiuent are synthesized, separating from the eiiiuent from the last-named converting step the butadiene content thereof and also a fraction containing essentially said benzene, hydrogenating said benzene fraction with said hydrogen-containing fraction separated from the efliuent of said rst converting step to convert said benzene to cyclohexane, separating cyclohexane from the hydrogenation eiliuent, converting said cyclohexane to butadiene and ethylene by subjecting it to a temperature between 1050 and 1550 F. and a low pressure, recovering butadiene from the resulting eiiiuent andv also a fraction containing essentially 10 said ethylene formed in said last converting step, and feeding said ethylene fraction to said second converting step in admixture with said C: to Cs olefin fraction recovered from the eiiluent of said first converting step.

3. A process for converting ethane to butadiene, which comprises converting ethane by dehydrogenating sameat an elevated temperature and a low pressure to form ethylene and free hydrogen, separating from eiiiuents of said dehydrogenation a gaseous fraction containing free hydrogen so produced and a normally gaseous hydrocarbon fraction containing ethylene so produced, converting said ethylene-containing hydrocarbon fraction together with ethylene from a subsequent cyclohexane conversion hereinafter speciiied at-an elevated temperature and a low pressure to produce an optimum yield of butadiene together with a substantial amount of benzene, recovering from eiiiuents of said conversion butadiene so produced as a product of the process, recovering also from etiluents of said conversion benzene incidentally produced, hydrogenating said benzene with free hydrogen from said gaseous hydrogen-containing fraction to produce cyclohexane, converting said cyclohexane at an elevated temperature and low pressure to produce an optimum yield of butadiene together with a substantial amount of ethylene, recovering from eiliuents of said conversion butadiene so produced as a product of the process, recovering also from effluents of said conversion ethylene incidentally produced, and admixing said ethylene with the aforesaid normally gaseous hydrocarbon fraction containing ethylene to form the feed to second-named converting step.

JEAN P. JONES. 

